Condition control reversible motor system

ABSTRACT

A condition control reversible motor system operates to rebalance a bridge circuit by means of a feedback potentiometer, the potentiometer wiper providing the energization potential to the bridge circuit. A reference voltage source and a lightly back-biased diode are connected to the bridge circuit in order to insure that the system always drives to a preferred or safe end in the event that the feedback potentiometer wiper open-circuits from the potentiometer resistive element due to dirt or some other defect.

United States Patent [1 1 Kabat CONDITION CONTROL REVERSIBLE MOTORSYSTEM [75] Inventor: John L. Kabat, Bloomington, Minn. [73] Assignee:Honeywell Inc., Minneapolis, Minn. [22] Filed: Feb. 20, 1973 [21] Appl.No.: 333,584

[52] U.S. Cl. 318/295, 318/663 [51] Int. Cl. G05b 1/06 [58] Field ofSearch... 318/294, 295, 471, 563, 663,

[56] References Cited UNITED STATES PATENTS 5/1973 Pinckaers 318/295 X10/1972 Uchida 9/1968 Doucette 318/663 X PREFERENTIAL BIASING BRIDGE REBALANCE Jan. 29, 1974 5 3,323,031 5/1967 Kasper et a1 318/295 X PrimaryExaminer-Bemard A. Gilheany Assistant Examiner-W. E. Duncanson, Jr.

Attorney, Agent, or Firm-Lamont B. Koontz; Omund R. Dahle [57] VABSTRACT A condition control reversible motor system operates torebalance a bridge circuit by means of a feedback potentiometer, thepotentiometer wiper providing the energization potential to the bridgecircuit. A reference voltage source and a lightly back-biased diode areconnected to the bridge circuit in order to insure that the systemalways drives to a preferred or safe end in the event that the feedbackpotentiometer wiper open-circuits from the potentiometer resistiveelement due to dirt or some other defect.

6 Claims, 2 Drawing Figures MOTOR CONTROL ELECTRONIC MOTOR cournor.

CONDITION CONTROL REVERSIBLE MOTOR SYSTEM BACKGROUND AND SUMMARY OF THEINVENTION In the copending application, Ser. No. 273,245 filed July 19,1972 in the name of B. Hubert Pinckaers, and assigned to the sameassignee as the present application, now U.S. Pat. No. 3,731,173 it istaught that in condition controlled reversible motor systems using afeedback potentiometer it is very desirable to provide some means tocause the motor system to drive to a preferred or safe position in theevent that dirt or some other material builds up on the feedbackpotentiometer causing the wiper to lift from the potentiometer resistiveelement. This type of defect is not uncommon in motor feedbackpotentiometer systems, and many times the open-circuit causes a huntingeffect which eventually leads to an open-circuiting either of the wiperconnection or of the potentiometer resistance itself. In the copendingapplication the emergency drive signal to the system is provided from aspecial output of the dual amplifier, which output is energized when thebridge voltage fails. A normally backbiased diode isolates this specialoutput from thebridge except when the wiper lifts and the energizingpotential is lost from the bridge.

The present invention is directed to a modification of this type ofsystem in which a reference voltage is connected through a diode to thebridge. The diode normally is back-biased in that the reference voltageis slightly less than the normal voltage range of the bridge point towhich the diode is connected.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic representation ofa bridge controlled reversible motor control system utilizing dualoperational amplifiers to control the motor in response to a sensedcondition; and

FIG. 2 shows a modification of the bridge of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In general terms the systemshown in FIG. 1 comprises an electrical condition responsive bridgecircuit which provides control signals to a dual preamplifier 11 whichin turn controls an electronic motor control system 12. The reversiblemotor 13 positions a load, here shown as valve 14, and also mechanicallydrives the wiper of a feedback potentiometer in the bridge circuit. TheMotor Control A conventional alternating current voltage source isconnected at terminals 15 and 16 to energize an electronic motor controlcircuit 17 and the motor 13. The details of this electronic motorcontrol form no part of the invention and are not shown in detail but ifdesired may be of the type shown in the copending application aboveidentified. A source of direct current voltage is connected acrossconductors 20 and 21 to energize the remainder of the circuit. Thisvoltage is obtained in any conventional way such as by rectifying thealternating current potential source.

The Dual Amp The control system utilizes a dual operational amplifier 11that has been disclosed schematically in a conventional manner at 23.The voltage source between conductors 20 and 21 supplies energy onconductors 35 and 36 to energize the dual operational amplifier 23. Theamplifier 23 has sections designated as A and'B. A non-inverting inputterminal for the A section is disclosed at 26, while the non-invertinginput terminal for the amplifier B is disclosed at 27. The invertinginput terminal for amplifier A is disclosed at 28 and for amplifier B at30. The dual operational amplifier may be of several commerciallyavailable types, such as the RC4558 commercially marketed by RaytheonCorporation. It may also be of the type generally known in the industryas the 747 type. Feedback resistors 31 and 32 around the amplifiers Aand B, respectively, cause these amplifiers to operate as switches. Theamplifier sections provide digital outputs, the first which may betermed the off,0 or low state and the second may be termed the on, 1 orhigh" state. When the output from amplifier A is high the motor iscaused to drive the valve toward the closed position. When the outputfrom amplifier B is high the motor is caused to drive the value 14toward the open position.

The Bridge The voltage source 20, 21 supplies energy to the conditionresponsive bridge voltage divider network generally disclosed at 10.This network includes a rebalance potentiometer 41 made up of apotentiometer resistor 42 and a potentiometer wiper 43, with thepotentiometer wiper 43 being directly connected to the conductor 20. Thepositive voltage is thus applied to the bridge through the wiper 43. Theleft hand portion of the bridge includes a part of the potentiometerresistance 42, a fixed resistor 44, a junction or output terminal 46, afixed resistor 45, and a portionof a potentiometer resistor 48 of acontrol potentiometer generally shown at 47. The control potentiometer47 also includes a potentiometer wiper 49 which is directly connected tothe negative conductor-21.

The right hand portion of the bridge includes a portion of thepotentiometer resistor 42, a fixed resistor 50, a fixed resistor 51, afixed resistor'52, and a portion of the potentiometer resistor 48. Abridge output terminal is between resistors 50 and5l, and a bridgeoutput terminal 54 is between resistors 51 and 52. The bridge outputterminal 46 is directly connected to the inverting input terminal 26 ofthe amplifier section A and to the non-inverting input terminal 30 ofthe amplifier section B. The bridge output terminal 53 is directlyconnected to the non-inverting input terminal 28 of the amplifiersection A. The output terminal 54 of the bridge is directly connected tothe non-inverting input terminal 27 of the amplifier section B. Theinput terminals 26 and 28 of amplifier section A are actually internallyconnected to the base electrodes of two transistors making up adifferential amplifier input circuit within the op. amp. Amplifierterminals 27 and 30 of amplifier section B are internally connected in asimilar fashion. The amplifiers A and B are responsive to the I polarityof and magnitude of signal unbalance at the differential amplifier stageinput terminals rather than to the absolute voltage level at the inputterminals. The Preferential Bias Circuit The preferential biasingcircuit shown at the left portion of the schematic is, in effect, asource of constant reference potential. In the specific embodimentshown,

the preferential biasing circuit is in the form of a voltage dividercomprising a resistor 60, a junction 61, a resistor 62, a junction 63and a resistor 64. This voltage divider is energized from a regulated DCvoltage source such as across conductors and 21 thereby providing asource of constant reference potential at junction 61 and junction 63. Abattery or the like could supply the constant voltage potential in placeof the voltage divider. The resistor values 60, 62 and 64 areselectively chosen so that the voltage at junction 61 is slightly higherthan the voltage at junction 53 of the bridge 10. A diode 65 isconnected between the junctions 61 and 53 with the direction of easycurrent flow being toward junction 61. The existing potentials thusnormally lightly back-bias diode 65. A diode 66 is connected between thejunctions 63 and 46 with the direction of easy current flow of diode 66being toward junction 46. The potential at junction 63 is chosen to beslightly less than the normal potential at junction 46 so that the diode66 is normally lightly back-biased. The backbiased diodes 65 and 66present an essentially infinite impedence to the bridge 10 so that undernormal conditions the preferential biasing circuit is effectivelyisolated from and does not place any electrical load or connection tothe bridge'circuit. Operation Under Normal Conditions In general, whenthe bridge unbalances in a direction such that input 26 is positive withrespect to input 28, the output of amplifier section A goes high tendingto drive the valve in a closed direction. When the opposite direction ofbridge unbalance occurs such that input terminal 27 is positive withrespect to input terminal 30, the output of amplifier section B goeshighdriving the motor in the opposite direction tending to open thevalve 14. It can thus be seen that if a control signal moves the wiper49 a predetermined distance toward the right along the resistive element48, the direction of bridge unbalance will be in a direction to turn onthe amplifier A and again to drive the valve 14 toward a closedposition. Simultaneously t e rebalance potentiometer wiper'will bedriven towa d the right until the error signal-from the bridge isreduced to zero. Under all normal operating conditions the diodes 65 and66 remain reverse biased, and the preferential biasing circuit plays nopart in the operation of the 'motor control. Operation During BridgeFailure A bridge failure will occur if the wiper lifts from one of thepotentiometers 41 or 47 or both. This failure may be caused, forexample, by accumulated dirt. It will be shown that in any of theseconditions the motor always drives the valve in one direction. If thewiper 43 lifts away from the resistive element 42 of the potentiometer41, the positive potential is removed from the bridge and the entirebridge potential tends to fall towards the negative voltage 21. Theconstant reference potential at point 63 now forward biases the diode 66to maintain the junction 46 positive at a voltage level about 0.6 voltsbelow the reference voltage. From terminal 46 a voltage divider pathexists through the resistors 44, 42, 50, 51, 52, and a portion of 48 tothe wiper 49. The amplifier A is receiving a potential on input 26 whichis positive with respect to input terminal 28, thus causing the motor todrive the valve toward the closed position. At such time as the wiper 43makes contact again with resistor 42, normal operation is resumed.

If wiper 49 lifts from the resistive element 48 of the potentiometer 47,the entire bridge tends to move toward the potential of the positivesupply 20. A constant reference potential at junction 61 now forwardbiases the diode 65 and current flows from the junction 53 through thediode 65 to the junction 61 to maintain the junction 53 at a voltagelevel about 0.6 volts above the reference voltage. A voltage dividercurrent path exists from the positive conductor 20 through wiper 43, theleft portion of resistor 42, resistors 44, 45, 48, 52 and S1 to thejunction 53 and then through the diode 65. The junction 46 is againpositive with respect to the junction 53 and amplifier A again causesthe motor to drive valve 14 toward a closed position.

In the more unlikely event that both wipers 43 and 49 lift from theirrespective potentiometer resistors, the preferential biasing circuitstill causes the motor to drive the valve 14 in a closed direction. Inthe operational amplifiers 23 the input terminals 26 and 28 connect tothe base electrodes of the transistors of a differential amplifier. Theemitter electrodes of the transistors are connected through theconductor 36 to the negative potential 21 so that a current path can betraced from the bridge and amplifier to negative. Thus the potential ofthe bridge 10 tends to be drawn toward the negative voltage 21. In thisevent the diode 66 is forward biased to maintain the terminal 46 andinput terminal 26 positive with respect to input 28 and again the motordrives the valve 14 toward the closed position.

FIG. 2 shows a modification of the bridge in which there is only onepotentiometer 41. The lower portion of the bridge has a conditionresponsive element 70 connected to the negative conductor 21, and thelower terminal of resistor 52 is connected to the same terminal. Thissystem operates in the same way as the system shown in FIG. 1. Sincethere is only one potentiometer wiper 43 which could lift, however, onlyone diode 66 is required to provide the emergency bias protection.

The embodiments of the invention in which an exclusive property or rightis claimed are defined as follows:

1. Preferential bias for the bridge circuit of a motor control system tocause the motor to drive in a predetermined direction in the event ofaloss of normal control signal comprising: I

a condition responsive bridge circuit having output terminals adapted toprovide control signals to electronic motor control means, said bridgecircuit including potentiometer means having a resistive element and awiper contact adjustable therealong;

a source of unidirectional energizing potential;

bridge circuit power input terminals, one of said input terminals beingconnected to said wiper contact of said potentiometer means forproviding said energizing potential to said bridge circuit through saidwiper contact, to provide a normal voltage range at a first of saidoutput terminals; said bridge circuit sometimes being subject to anundersirable faulty operating condition in which said wiper losescontact with said resistive element and the bridge circuit does notreceive energizing potential whereupon the control signal fails;reference voltage means; and normally non-conductive diode meansconnected between said bridge circuit and said reference voltage means,which reference voltage means is of a magnitude to normally slightlyback-bias said diode means, said back-biased diode means thus normallypresenting a high impedance to said bridge circuit, until the occurrenceof said wiper losing contact with said resistive element thusdeenergizing said bridge circuit whereupon said diode means is forwardbiased by said reference voltage to provide a predetermined emergencycontrol signal to said electronic motor control system.

2. The invention according to claim 1 in which the source of referencevoltage comprises impedance voltage divider means having at least onereference voltage tap.

3. The invention according to claim 1 in which the diode means isconnected to the bridge circuit at a bridge output terminal.

4. The invention according to claim 1 in which said bridge circuitincludes a second potentiometer means connected on the opposite side ofthe bridge from the first mentioned potentiometer means and in which theother power input terminal is connected to the wiper contact of thesecond potentiometer means so that the potential to said bridge isapplied through two potentiometer wipers.

5. The invention according to claim 4 in which said diode meanscomprises a first and a second diode, the first and second diodes beingpoled in-opposite directions, the first diode being connected to onebridge output terminal and the second diode being connected to the otherbridge output terminal, and both diodes being normally back-biased.

6. In an electronic motor control system of the type having a conditionresponsive bridge circuit providing control signals, the bridge circuitincluding potentiometer means having a resistive element and a wipercontact adjustable therealong, the bridge circuit being energized by asource of unidirectional potential which is connected to the wipercontact for providing energizing potential to the bridge circuit throughthe wiper contact, the bridge circuit sometimes being subject to anundersirable faulty operation condition in which the wiper loses contactwith the resistive element and the bridge circuit does not receiveenergizing potential, the system requiring an emergency control signalin such condition to drive the motor in a predetermined direction,

the improvement comprising: a source of reference voltage and normallynonconductive diode means connected be tween the bridge circuit and saidsource of reference voltage, the reference voltage being of a magnitudeto slightly back-bias said diode means normally thus normally presentinga high impedance to said bridge circuit and in effect isolating saidsource of reference voltage from said bridge circuit, until theoccurrence of said wiper losing contact with said resistive element thusdeenergizing said bridge circuit whereupon said diode means is forwardbiased by said reference voltage to provide a predetermined emergencycontrol signal to said electronic motor control system.

1. Preferential bias for the bridge circuit of a motor control system tocause the motor to drive in a predetermined direction in the event of aloss of normal control signal comprising: a condition responsive bridgecircuit having output terminals adapted to provide control signals toelectronic motor control means, said bridge circuit includingpotentiometer means having a resistive element and a wiper contactadjustable therealong; a source of unidirectional energizing potential;bridge circuit power input terminals, one of said input terminals beingconnected to said wiper contact of said potentiometer means forproviding said energizing potential to said bridge circuit through saidwiper contact, to provide a normal voltage range at a first of saidoutput terminals; said bridge circuit sometimes being subject to anundersirable faulty operating condition in which said wiper losescontact with said resistive element and the bridge circuit does notreceive energizing potential whereupon the control signal fails;reference voltage means; and normally non-conductive diode meansconnected between said bridge circuit and said reference voltage means,which reference voltage means is of a magnitude to normally slightlyback-bias said diode means, said back-biased diode means thus normallypresenting a high impedance to said bridge circuit, until the occurrenceof said wiper losing contact with said resistive element thusde-energizing said bridge circuit whereupon said diode means is forwardbiased by said reference voltage to provide a predetermined emergencycontrol signal to said electronic motor control system.
 2. The inventionaccording to claim 1 in which the source of reference voltage comprisesimpedance voltage divider means having at least one reference voltagetap.
 3. The invention according to claim 1 in which the diode means isconnected to the bridge circuit at a bridge output terminal.
 4. Theinvention according to claim 1 in which said bridge circuit includes asecond potentiometer means connected on the opposite side of the bridgefrom the first mentioned potentiometer means and in which the otherpower input terminal is connected to the wiper contact of the secondpotentiometer means so that the potential to said bridge is appliedthrough two potentiometer wipers.
 5. The invention according to claim 4in which said diode means comprises a first and a second diode, thefirst and second diodes being poled in opposite directions, the firstdiode being connected to one bridge output terminal and the second diodebeing connected to the otHer bridge output terminal, and both diodesbeing normally back-biased.
 6. In an electronic motor control system ofthe type having a condition responsive bridge circuit providing controlsignals, the bridge circuit including potentiometer means having aresistive element and a wiper contact adjustable therealong, the bridgecircuit being energized by a source of unidirectional potential which isconnected to the wiper contact for providing energizing potential to thebridge circuit through the wiper contact, the bridge circuit sometimesbeing subject to an undersirable faulty operation condition in which thewiper loses contact with the resistive element and the bridge circuitdoes not receive energizing potential, the system requiring an emergencycontrol signal in such condition to drive the motor in a predetermineddirection, the improvement comprising: a source of reference voltage andnormally non-conductive diode means connected between the bridge circuitand said source of reference voltage, the reference voltage being of amagnitude to slightly back-bias said diode means normally thus normallypresenting a high impedance to said bridge circuit and in effectisolating said source of reference voltage from said bridge circuit,until the occurrence of said wiper losing contact with said resistiveelement thus de-energizing said bridge circuit whereupon said diodemeans is forward biased by said reference voltage to provide apredetermined emergency control signal to said electronic motor controlsystem.